Major problems in using oils from renewable feedstocks such as plant oils, (i.e. soybean oils and other vegetable oils), or oils or fats derived from animal sources, (e.g. menhaden, lard, butterfat and other animal derived oils) as various type lubricants are: (1) their low oxidative stability; (2) their relatively low viscosities; and (3) tendencies to solidify at low operating temperatures as manifested by relatively high pour points (temperatures below which they will no longer pour). However, successful modification of animal or vegetable oils or fats that overcomes these liabilities should reduce the U.S. dependence on foreign oil, since these lubricant candidates would be derived from renewable feedstocks. Lubricants derived from renewable feedstocks are also typically biodegradable. A typical renewable feedstock oil is represented by soybean oil. In fact, soybean oil is a preferred oil due to its high availability and relatively low cost.
An important driver towards the use of biodegradable lubricants is the worldwide misuse of mineral based lubricants. Of the approximately 1200 million gallons of lubricants used in Europe in 1990, about 170 million gallons (13%) disappeared into the environment. In the United States, of the approximately 1350 million gallons used about 430 million gallons (32%) ended up in landfills or were dumped. Recent studies from 2002, estimate that about 50% of lubricants worldwide end up in the environment.
Erhan, et al (U.S. Pat. No. 6,583,302 hereafter referred to as Erhan) discloses that vicinal diesters of plant oil triglycerides can be produced by reacting epoxidized triglycerides (e.g. epoxidized soybean oil) by a two-step and a one-step procedure. In the two-step procedure, epoxidized soybean oil is reacted with water in the presence of the Bronsted acid perchloric acid to produce putative vicinal diols along the fatty acid chains. This mixture is then reacted with various acid anhydrides to produce putative vicinal diester structures along the fatty acid chains.
Based on literature precedents, the amount of vicinal diester products of the type shown above obtained by either of the two processes is believed to be about 25%. The majority (about 75%) of the product is expected to consist of tetrahydrofuranyl (oxolane) substructures bearing two ester groups.
It is well known and described in the open literature that methylene-interrupted bis-epoxides will generate tetrahydrofuranyl diols in nearly quantitative yields when reacted with water in the presence of either Bronsted or Lewis acids.
Thus, in a two step process (which uses a Bronsted acid), the tetrahydrofuranyl diols would be produced from linoleate and linolenate fatty acids (each of which have methylene-interrupted bis-epoxide structures) and these diols would then be acylated to form tetrahydrofuranyl diesters.
Erhan's one step process uses the Lewis acid catalyst boron trifluoride and this one step process uses acid anhydride without the involvement of water. It is presently believed that the same tetrahydrofuranyl structures that are formed in two-step process are also formed in the one-step approach since Erhan's patent implies that products obtained by both processes have similar NMR spectra. Also, both the microoxidation and pressurized differential scanning calorimetry data from the two-step and the one-step process are very similar. Also, the microoxidation results reported by Erhan show very significant percent volatile loss and percent insoluble deposit that is very much higher than those reported in the present invention where vicinal diesters are actually produced. These high oxidative decomposition pathways are consistent with tetrahydrofuranyl ring structures that are known to be very susceptible to oxidative decomposition.
In epoxidized soybean oil, approximately 75% of all epoxide groups are of the methylene bis-epoxide type and will thus produce the tetrahydrofuranyl diester system under both reaction approaches described by Erhan.
In contrast to Erhan, the present invention uses basic catalysts to convert epoxidized soybean oil to substantially quantitative amounts of vicinal diesters while avoiding formation of the tetrahydrofuranyl (oxolane) ring structure.
U.S. Pat. No. 5,623,086 to Perri et al discloses a process for producing 1,2-bis(acyloxylates) that are useful with the invention.